The present invention is directed toward a method and apparatus for monitoring a tool in a press. It is important to monitor the condition of a tool to determine when the tool has failed, and to prevent a subsequent press stroke which can lead to catastrophic failure. Unfortunately, monitoring the condition of the tool is not easy due to the harsh operating environment. Several methods of monitoring tools have been proposed, each having its own drawbacks.
U.S. Pat. No. 3,444,390 discloses a press impact sensor which is mounted to a platen beneath a lower die. The sensor is a piezo-electric sensor which converts pressure or shock waves into electrical signals. The sensed signals are compared to a reference signal and, when the signals fall outside a predetermined normal range, the press is shut down to prevent a subsequent strike. U.S. Pat. Nos. 3,930,248 and Re. 30,298 disclose a similar piezo-electric control circuit. U.S. Pat. No. 4,023,044 discloses a similar pressure monitoring arrangement for a punch press.
U.S. Pat. Nos. 4,936,126; 4,987,528; 4,918,616; 4,750,131; 4,698,991; 4,651,273; 4,633,720; and 4,593,547 disclose methods for sensing die pressure and defective parts.
U.S. Pat. No. 3,555,865 discloses a press having an upper die, a lower die, a fixed anvil or platen, and a sow block disposed between the lower die and the fixed platen. The platen has a series of passageways formed therein through which hydraulic fluid flows to an area between the sow block and the platen to form a cushioning film therebetween.
There exists a need in the art for a simple and reliable method and apparatus for sensing failure of a tool in a press. There also exists a need in the art for a method for controlling a press to prevent a subsequent stroke in the event of tool failure.